HomeMy WebLinkAboutWPO202200028 Correspondence 2023-03-17SHIMP ENGINEERING, P.C.
Design Focused Engineering
March 10, 2023
John Anderson, PE,CFM
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter for WPO2022-00028 River's Edge — VSMP
Dear Mr. Anderson,
Thank you for your review of the VSMP Plans for River's Edge. We have revised the plan per your most
recent comments dated July 17, 2022. Please find below a detailed response to each of your comments.
A. Stormwater Pollution Prevention Plan (SWPPP)
The SWPPP content requirements can be found in County Code section 17-405. A SWPPP must contain
(1) a PPP, (2) an ESCP, (3) a SWMP, and (4) any TMDL measures necessary.
1. Please ensure SWPPP cover includes reference to WPO2021-00069.
SWPPP cover sheet includes reference to WPO2021-00069.
2. Submit SWPPP using county template located at:
https://www,albemarle.org/home/showpublisheddocument/ 166/637202310327530000
County SWPPP Template used.
Sec. 1: Registration Statement; please complete.
The Registration Statement to be completed next submission.
b. Sec. 6.A.: PPP Exhibit: Please show initial location of.
i. Rain gauge.
Rain gauge locations provided.
ii. Portable sanitary facilities (ports John), as required.
Porta-John locations provided.
iii. Covered non -hazardous waste dumpster, if required.
Solid waste dumpster locations provided.
iv. Vehicle wash waters, draining to trapping measure (Not a sediment trap design,
per se, but shallow depression— 1-2 backhoe buckets. Avoid direct drainage to
Ex. stone system, or pond/s.)
Vehicle wash waters drain to sediment trap #1.
v. Concrete wash -out.
Concrete washout locations provided.
vi. On -site fuel, if required.
On -site fuel storage locations provided.
vii. Paint, stucco, chemical storage, if required.
Chemical storage provided for phase 2.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
c. Sec. 6E: List named individual responsible for PPP measures.
The individual responsible for PPP measures will be provided next submission.
d. Sec. 8: List named individual responsible for ESC inspections, qualified to evaluate
compliance relative to VESCH, 31 Edition, 1992.
The individual responsible for ESC inspections will be provided next submission.
e. Sec. 9: Ensure Signed Certification is signed and dated.
The Signed Certification will be signed and provided next submission.
& Pollution Prevention Plan (PPP) — See above, item 2.b.
The PPP content requirements can be found in County Code section 17-404.
C. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a
SWMP. This plan is disapproved for reasons listed below. The stormwater management plan content
requirements can be found in County Code section 17-403.
1. Provide SWM design
a. Initial submittal does not include specific SWM plan or design information either for
underground detention, or dry pond 1.
SWM profiles are provided on Sheets C15 & C16 of the revised VSMP plan,
including profiles for both sections of the underground detention system and dry
pond. Revisions have been made to the underground detention system and the
profiles have been updated accordingly. Additionally, more detail has been added
to the underground detention profiles to include necessary stone placement and
installation details.
b. Include:
i. SWM design details, plan /profile, for underground detention system and dry
pond. Partial profile of UG detention is insufficient for review, construction,
bonding, or inspection purposes.
Sheets C15 & C16 include detailed profiles of the underground detention
system. The underground detention system has been revised and the
profiles have been updated accordingly. Additionally, more details have
been added to the profile to include necessary stone placement and
installation details.
ii. Ensure SWM facility profiles are specific to site; show existing and proposed
grade.
SWM Facility profiles are provided on Sheets C15 & C16 with existing and
proposed grades included.
iii. Include SWM facility access to dry pond (10' width; max. slope 20%).
A 20-ft SWM Facility Access Easement has been provided to the dry pond.
iv. Label all pipe riprap outlet protection dimensions (L x W x D) incl. dry pond
inlet pipes.
Riprap outlet protection dimensions provided.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
v. Note: Platted SWM facility and public drainage easements (each on -site SWM
facility) must be recorded prior to WPO plan approval. Please submit SWM
public drainage easement plat at earliest convenience.
Easement plat recordation will be provided with a future submittal.
vi. Include SWM facility (typical) construction, maintenance, and inspection
information for dry pond and underground (Mfr.) detention systems.
Underground SWM Facility construction, maintenance and inspection
information has been provided on Storrawater Management Plan, Sheet
C14. Dry detention pond construction and maintenance notes are provided
on Sheet C14.
vii. Include Construction Record Drawings (As -built for VSMP policy on the plan.
The Construction Record Drawings for VSMP policy has been provided on
Sheet C2 and a note has been added under General Notes on Sheet C1
specifying that these items must be completed.
2. ZMA201800018 Application Plan, 14 Apr 2020, shows normal crown site access with storm
inlets and pipe conveyance, not 4' ditch section (09). Revise and provide DI -pipe
conveyance per approved ZMA Application plan. Design must minimize potential impacts
to preserved steep slopes, and pipe conveyance is less likely to present future EP or roadside
erosion than grass -lined ditches. Ref. approved ZMA Application plan, pp 20-22, as well as
1-Apr 2022 initial site plan Engineering review comments, item 6.f. Also, 14-410.G./18-
32.7.2.2.a Pipe /DIs are deemed necessary to limit erosion of (site access) pavement, and to
minimize impacts to preserved steep slopes situated below site access that is more likely to
occur with grass -lined SCC. Note: Critical safety issue: at different points both sides of site
access falls away to steep, unrecoverable slopes. CG-6 with minimal flat area beyond curb
provides wheel -strike barrier to off- road incident, whereas ditch section without shoulder
does not. Proposed site access provides SCC nearly immediately adjacent to paved surface
(SCC itself a hazard) without shoulder with intermittent drops to steep unrecoverable slopes.
Site access design is problematic from safety, drainage, and prior -approval standpoints.
Substantial additional guardrail is requisite with current design (no curb), with placement of
SCC checked against guardrail and space constraints, but this point is likely irrelevant as
WPO plan must conform with ZMA Application plan and ordinance requirements for
adequate drainage and ordinance mandate to minimize potential impact to preserved steep
slopes.
The ZMA appears to shows roadside ditches to DI-7 grate drop inlets (not
curb/gutter). Ditches are provided all along the road sides and include a 2-ft shoulder.
A 2-ft shoulder was chosen to minimize disturbance of steep slopes. Further, the road
entrance has been relocated and as a result provides for much less steep slope
disturbance. This comment was discussed with John Anderson during a meeting on
November 11, 2022 and was resolved to be appropriate to provide ditches to grate drop
inlets.
3. C9 (Also related to ISP): Locate 3" FM outside edge of (site access) pavement, consistent
with approved ZMA Application Plan sheet 12. FM located within /beneath pavement limits
access to utility and access to residences for Rivers Edge residents in event of FM break,
repair, or replacement. If site access stone design is revised to provide DI/pipe conveyance,
it should be possible to locate FM opposite pipe (other side of travelway), or possibly in
same utility trench as stone pipe, with offset, as needed. SP201800023 includes Preliminary
Central Sewage System Plan for River's Edge. This plan shows 3" FM outside paved
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
surface of site access. Revise plan per approved ZMA Application Plan and SP201800023
Preliminary Central Sewage System Plan for River's Edge.
The sanitary forcemain has been relocated outside of the pavement along the access
road.
4. C10
a. Ref. ISP Engineering review comment (4/l/22), item 6.e., and revise CIO 340 LF UG
detention system, per ISP comment. See ISP comment for rationale. Design shows no
change to proposed UG detention system in response to April 2022 ISP review
comment, which may cause delay. As noted in ISP review item 6.e., proposed 340 LF
UG detention is inconsistent with approved ZMA Application plan, and will not be
approved. Additional comments possible with revised design.
The proposed detention system has been broken up into 2 separate sections that
will allow for maintenance and replacement of 1 section while still providing access
and parking in the lower section.
b. Engineered Level Spreader (ELS) downslope of 340 LF UG does not meet VA DEQ
Stormwater Design Specification No. 2 Table 2.2 Min. width /Max. slope requirements,
or Max. L if designed to transition 10-yr concentrated post-dev UG detention discharge
to sheet flow (Also, item 4.e.i. below). An ELS in this location appears incapable of
meeting ELS design criteria. Please see Engineering ISP review item 2.c., and revise
design. Proposed 5' trail near the river (downslope of proposed ELS) will likely
experience erosion with proposed design since discharge from ELS to slopes is
anticipated to cut /create new drainage patterns as it traverses slope and reaches/transits
proposed trail. Please provide storm pipe across preserved slopes to edge of N. Fork
Rivanna River (storm pipe across preserved steep slopes is permissible provided no
other alternative exists; none appears to); storm discharge at this location should be
evaluated to ensure it meets energy balance requirements with outfall protection
designed per VESCH Std. & Spec.3.18. 59-p. Calculation packet, p. 1, indicates
discharge from the new UG detention system `releases the 1-yr storm at rates complaint
with the Energy Balance Equation,' in which case, it is simply a matter of conveying
detention system discharge via pipe across slopes, beneath trail to the river. See design
for dry pond outfall pipe which extends to edge of N. Fork Rivanna River. Additional
comments possible with revised design.
The level spreader has been removed from the plans and a discharge pipe is now
proposed to the edge of the N. Fork Rivanna River.
C 14: Provide profile for ELS to correspond with Calc. packet, p. 1 statement: `This
runoff will be released to a Level Spreader which will convert the concentrated flow to
sheet flow across a 1.77% slope for 112-ft before reaching the river banks.'
The level spreader is no longer proposed on these plans.
d. Provide SWM narrative and design conveyance for site discharge across 5' trail. Please
note calc. packet pg.I peak discharge POA 1 table value, 56.52cfs. Design cannot
predict with reliable assurance that 56.52 cfs during the 10-yr event will sheet flow
across the 5' trail without significant erosive effect. As mentioned elsewhere, sheet flow
on even moderate slopes tends to reconcentrate and establish drainage patterns that
would likely subject the 5' trail to persistent or intractable erosion or maintenance
issues. Design should route site discharge beneath trail to river edge. Ref. ZMA
Application, sheet 23, which shows discharge at N. Fork Rivanna River edge.
Eliminating an ELS at this location also eliminates issues that typically attend ELS
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
construction/maintenance. Any measurable departure from 0.0% grade for an ELS
typically causes an ELS to discharge not as sheet flow, but at the low point along an
ELS, as concentrated flow.
The level spreader has been removed from the plans and the discharge pipe is now
proposed to the edge of N. Fork Rivanna River.
Calculation packet
i. Flood protection, POA 1: Clarify how post-dev 10-yr release rate (56.52 cfs)
meets 9VAC25-870-66.C. requirements. Also, ELS design problematic if post-
dev 10-yr peak flow =56.52 cfs. (ELS design criteria [VA DEQ Spec. No. 2,
Table 2.2] requires 131f ELS /cfs, with 130' Max. ELS Length). Note: POA 1
post-dev 10-yr discharge is higher than pre-dev POA 1 pre-dev discharge, but
POA 1 may still comply with 9VAC25-870-66.C.2. via conveyance design that
confines the post -development peak flow rate from the 10-year 24-hour storm
event within the stormwater conveyance system.
The Post-Dev 10-yr release rate meets the Flood Protection requirements
under 9VAC25-870-66.C.3.0 which states, `The stormwater conveyance
system enters a mapped floodplain or other flood -prone area, adopted by
ordinance, of any locality.' The 10-yr storm is proposed to be released into
a mapped floodplain and therefore meets this requirement.
ii. Additional comments possible since Engineering anticipates site access drainage
design and SWM UG detention design to change.
Acknowledged.
iii. Graphic, p. 4 and 17, Calc. packet, POA 1 does not align with plan UG
detention point of discharge (C 12, C 13); revise Calc. packet graphics to
accurately depict post-dev UG detention point of discharge. Revise calc. tables,
as needed.
An exception letter has been provided with this submission requesting an
exception to the location of the point of analysis. Energy balance equation
could not be met at the point of discharge without an unreasonable level of
detention. Energy balance equation is met 970-ft downstream of discharge
location where the pre -development area drains to. In the exception
request letter, it is explained that releasing the runoff at this discharge
location will not contribute to erosion. Further, piping the discharge to the
POA will only increase the disturbance in the flood plain and steep slopes
while not providing any real benefit to erosion prevention in the North
Fork Rivanna River.
iv. Pg.24:
1. Increase pipe diameter or slope, F2 to F 1 since 10-yr peak flow
(32.51cfs) is 98.8% of pipe capacity. For less frequent events, there is
no relief if pipe capacity is exceeded; drive aisle to lower lot will
experience excess runoff flooding.
The pipe diameter has been increased to 24" to provide greater
capacity.
2. Recommend:
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
a. Increase pipe diameter or slope, 172C to 172B. (18" HDPE pipe,
0.90% slope is at 98.4% capacity for 10-yr event)
The pipe diameter has been increased to 24" to provide
greater capacity.
b. Increase pipe diameter or slope, 17213 to 172A. (same; 98.4%
capacity)
The pipe diameter has been increased to 24" to provide
greater capacity.
5. CI 1: Ensure SCC inlet to dry pond 1 has riprap outfall protection to protect dry pond 1 floor
(similar to outlet protection shown at pipe inlet to dry pond 1).
Outlet protection has been provided in dry pond 1 from both the pipe in and the ditch
in. Rip rap is extended over the floor of the pond.
6. C 13: Provide storm conveyance (ditch to DI-7) behind CG-6 west of site access (travel way;
z contour 446'). Design spills runoff over curb onto pavement. Eliminate overland runoff to
paved surface. Engineering also recommends nominal width for pedestrians who may be
forced by circumstance to walk along site access. Note: Although existing driveway is
converted to a pedestrian path, this path will likely transit unlit remote forest. Any number
of residents may wish to avoid remote path at night /in darkness; in which case, residents
forced to walk the distance, Rt. 29 to their home may welcome a flat area more easily
accessible and highly visible adjacent to River's Edge primary site access.
The ditch has been extended past the CG-6 to capture runoff from the curb and gutter.
7. Show steep slopes on Site, Utility, and Grading Plan sheets, similar to floodplain and stream
buffer limits, which are shown, since design and impacts cannot be evaluated unless steep
slopes are delineated (shown/labeled).
Steep slopes hatch now shown on Site, Utility and Grading Plan Sheets. Sheet C8-C13.
8. C14: Wherever vertical difference between INV in and INV out exceeds 4', please provide
label on storm str. profile for %" steel plate in MH floor; str. F2 and F4, for example. [VDOT
Drainage Manual, p. 9-37, 9.4.8.7, Maximum Grades]
Notes have been added to the profiles to provide Y:" steel plates on manhole floor for
structures F2, F4, A2, A3.
A Erosion and Sediment Control Plan (ESCP)
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan
is disapproved for reasons listed, below. The erosion control plan content requirements can be found in
County Code section 17-402.
1. C19-C21
a. Show and label steep slopes.
The steep slopes are shown on Sheets C19-21.
b. Provide plan notes requiring contractor to:
i. Delineate /flag limits of preserved steep slopes which intersect LOD.
Note provided on Sheets C19-C21.
ii. Flag approved plan limits of disturbance within preserved slopes, the point
beyond which disturbance or impact to steep slopes may not occur.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
Note provided on Sheets C19-C21.
iii. Replace /maintain steep slopes delineation flagging for duration of project.
Note Provided on Sheets C19-C21.
2. C19
a. Show/label paved construction entrance at Rt. 29.
i. Revise PCE at Rt. 29 to show paved construction entrance beginning at edge of
shoulder, not edge of Rt. 29 thru travel lane.
Paved construction entrance shown and located at edge of shoulder.
b. Label ST 1 floor dimensions (LxW). Also, Sheet C22.
ST 1 floor dimensions provided.
3. C21
a. Label ST 3,4 floor dimensions (LxW). Also Sheet C24
Dimensions provided for ST 3 & 4 on Sheet C23 & C26.
4. C22
a. Show/label outfall riprap dimensions (15" HDPE, LxW) at N. Fork Rivanna River.
No riprap is proposed at the outfall into the North Fork Rivanna River. Rather
the final section of pipe will be extended slightly into the river with a shallow slope
that allows the river water to backflow up the pipe resulting in lower velocities.
b. Provide adequate temporary ESC measures for storm corridor to river (incl. VESCH
abbreviations for measures).
ESC measures provided for pipe to river.
5. C26
a. Revise sediment trap design table, ST4, to provide wet -dry storage volume for 1.83 ac.
(Phase 1) DA.
Sediment trap, ST4, now provides wet -dry storage volume for the 1.83 ac DA in
Phase 1.
b. Recommend provide 2 separate ST design tables, for ESC phase 1 and 2, since drainage
areas contributing runoff to sediment traps vary considerably, phase 1 to phase 2.
Ensure STs are sized appropriately, whether in phase 1 or 2.
Two (2) separate ST design tables have been provided on Sheet C28 for Phase 1
and Phase 2 designs. All sediment traps are sized appropriately.
6. Label ST floor dimensions on plan sheets, LxW (phase 1, phase 2).
ST floor dimensions provided on plan sheets.
`Next Steps' after WPO plan approval
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
1. Purchase Nutrient Credits (6.17 lb. nutrient credit purchase required)
a. Please coordinate with the County reviewer before working with a nutrient bank. The
reviewer must confirm if your project must follow the DEQ hierarchy requirements.
Acknowledged, we will coordinate with County regarding purchase of nutrient
credits.
b. Letter of Availability must be provided on the WPO approved plans.
Acknowledged, the Letter of Availability will be provided on the WPO approved
plans once received from nutrient bank
c. Applicant must contact/coordinate nutrient purchase with Ana Kilmer,
akilmer@albemarle.org.
Acknowledged, the nutrient purchase will be coordinated with Ana Kilmer.
d. Affidavit of Purchase must be provided to Ana Kilmer before a grading permit can be
issued.
Acknowledged, the Affidavit of Purchase will be provided to Ana Kilmer.
2. Post WPO Bond
a. Applicant must submit a Request to Establish a Bond form and fee to CDD.
i. Complete the form and email it to akilmer&albemarle.org along with proof of
payment (see below).
Acknowledged, the Request to Establish a Bond will be provided upon WPO
plan approval.
b. Payment can be made either online or with a check.
i. If paying online:
1. Go to online payment portal.
a. Select WPONSMP as the application `type'.
b. Type in the WPO number and project name in the Notes/Details
section of the form.
c. Type in the `payment amount' as $294.34.
d. Click "Proceed to Secure Checkout" link to make payment.
2. You will receive a receipt in an email.
ii. Email a copy of the receipt to akilmer@albemarle.org.
Acknowledged.
c. Once the bond request and payment are received, the applicant can provide the bond
estimate (completed on the County worksheet), or Engineering staff will complete the
estimate. Once the estimate is approved, Ana Kilmer will contact and work with the
applicant to post the bond.
Acknowledged, the bond request, payment and estimate will be provided to Ana
Kilmer.
3. Obtain DEQ Permit
After Nutrient credits have been purchased and the bond has been posted:
a. County staff will register the project with DEQ.
Acknowledged.
b. Applicant/operator listed on the Registration Statement will receive an email with
instructions on how to pay the DEQ permit fee.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
Acknowledged.
c. Applicant must email a copy of the DEQ receipt of payment to charriskalbemarle.org
Acknowledged.
d. DEQ typically will issue a permit within 2 weeks of receiving payment.
Acknowledged.
4. Request pre -construction meeting:
a. Complete and email the request for a preconstruction meeting and grading permit to
charris@albemarle.org.
Acknowledged, the request for preconstruction meeting and grading permit will be
provided in the future.
b. Pay the fee via the online payment portal or a check at the pre -construction meeting. If
paid online, email a copy of the receipt to charris&albemarle.org.
Acknowledged.
If you have any questions or concerns about these revisions, please feel free to contact me at
Michael@shimp-en ing eering com or by phone at 434-227-5140. You may also contact Justin Shimp at
Justin@shimp-en ing eering com.
Regards,
Michael Chandler
Shimp Engineering, P.C.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com